The invention relates generally to an earthmoving device in the form of a tractor-drawn scraper having a bowl into which the loosened soil is propelled by an elevator and which has improved means for dumping when the bowl is filled.
When operating under wet conditions in clayey soils the soil which is collected in the scraper bowl is not easily dislodged. It has been the practice in the past to employ a floor having a fixed rear section and a sliding front section which is shifted rearwardly to provide a discharge opening. The rear wall of the bowl is commmonly in the form of an ejector plate which is thrust forwardly by actuators to push the soil into a position over the front opening. The effect of the ejector plate is often to compact the soil into a tight mass which becomes firmly stuck to the side sheets of the bowl and tightly jammed into the flights of the elevator, both effects, combined with the relatively small area of the opening, tending to cause the soil to become "hung up" in the bowl. Moreover, it is found that when using bowls having a length which is greater than the width dimension, the tendency of the mass of soil to expand outwardly toward the side walls, in the case of clayey soils, produces a bracing effect which may be sufficient to block the ejector plate against further forward movement. Thus while conventional elevator type scrapers work very well in soils which are relatively dry and friable it is sometimes necessary, in the case of wet clayey soils, to suspend operations until the soil loses some of its moisture, which is both disruptive and costly.
Moreover, in the usual design of a sliding front floor section the section has rollers which are fitted in tracks or on rails formed at the lower edges of the bowl side sheets, in close proximity to the ground. In such vulnerable position the tracks are susceptible to clogging with clay, rocks or debris and to damage from boulders and the like. Moreover, because of the wide spacing between the tracks, there is a cocking tendency when more resistance is encountered on one side of the floor section than on the other. The actuators which operate the slidable floor section must be positioned low in the structure so that the forces which they apply are in line with the resistance, and such low positioning makes these devices, too, subject to damage and malfunction.
Because of the necessity for sliding the front floor section under the rear, fixed, floor section while achieving the necessary ground clearance, the fixed floor section must be located relatively high off the ground, which results in a sacrifice in carrying capacity and which tends to raise the center of gravity.
It is, moreover, a common expedient in devices of this type to mount the scraper blade at the front edge of the slidable floor section so that it, upon retraction, may also serve as a spreader or strike-off device. However, the modern tendency to use relatively narrow scraper blades with projecting ripper teeth to engage the subsoil precludes smooth, full-width strike-off or leveling. Also, when the scraper blade is mounted on the forward edge of a slidable floor section, the floor section and its mounting must be made quite massive in order to absorb reaction forces, but without imparting any strength to the bowl structure. Then too, where an ejector plate is used in lieu of a back wall, the side sheets do not have back wall for lateral bracing so that the bowl lacks reinforcement at the back as well as at the front. To this must be added the fact that, where an ejector plate is used, provision must be made behind the plate, and between the rear wheels, for relatively massive actuators and actuator mounting elements which, in the case of a scraper having a rear engine, results in serious space and design complications.